1. Field of the Invention
The present invention is related to an ultrasonic diagnostic device for performing a signal-analysis process on signal data that corresponds to ultrasonic echoes received from a subject and for creating and displaying image data regarding the subject, and a method of controlling the ultrasonic diagnostic device. In particular, the present invention is related to an ultrasonic diagnostic device for analyzing image data regarding a diagnostic target of said subject, and a method of controlling the ultrasonic diagnostic device.
2. Description of the Related Art
As described in Japanese Unexamined Patent Application Publication 2005-185731, an ultrasonic diagnostic device has been generally known that performs an analysis process, such as an FFT process, on signal data that corresponds to ultrasonic echoes from a subject using an ultrasonic pulse-reflection method or an ultrasonic Doppler method, in order to create and display image data regarding a diagnostic target of the subject, such as waveform data including a tomographic image of a diagnostic site of the subject and blood flow information thereof.
For a diagnosis with this type of ultrasonic diagnostic device, prior to the work for measuring a diagnostic index of the diagnostic target based on the image data regarding the diagnostic target of the subject (e.g. Doppler spectrum waveform data including blood flow information), it is necessary to first perform work for detecting image data corresponding to a diagnostic target of a subject. In other words, in a diagnosis with an ultrasonic diagnostic device, it is common to first go through the detecting phase, which is a phase of work for detecting such image data, before the measuring phase for measuring a diagnostic index based on the detected image data.
A Doppler spectrum waveform that visually represents valve regurgitation of the heart is displayed on the bottom of a display screen on the ultrasonic diagnostic device. The horizontal axis of this waveform indicates time and the vertical axis indicates the blood velocity at each moment. For this waveform, the polarity is set on the negative side (that is, the normal direction of blood flow is negative), and, of the waveforms, the waveform on the positive side represents valve regurgitation of the heart. The flow velocity for this valve regurgitation is fast, but the blood flow volume thereof is minute and the S/N ratio is not necessarily good, so it is assumed to be relatively difficult to detect.
The Doppler spectrum waveform data is created by a fast Fourier transformation (FFT) process. In the FFT process, the Doppler spectrum waveform data is created by extracting waveform data of time periods before and after each instance of sampling (the length of this time period is referred to as the observation time length), performing the FFT process on the waveform data of the time of extraction, calculating the Doppler spectrum of the time of sampling, and ranking the spectrum in chronological order. If the observation time length is not set appropriately for the FFT process, there may be a failure to detect and/or display, for example, a Doppler spectrum waveform on the positive side, (i.e. a waveform corresponding to valve regurgitation).
In the FFT process, there is a trade-off between velocity-detection sensitivity and time resolution. In other words, when the observation time length is set to be relatively long, it is able to obtain spectrums of a wide range of frequencies for the spectrum at each instance of sampling, therefore the velocity-detection sensitivity becomes higher, while the data in the time axis is leveled out and the time resolution decreases. On the other hand, when the observation time length is set to be relatively short, the velocity-detection sensitivity decreases, while the time resolution increases.
With these consideration in mind, it is desirable, in the detecting phase, to set the observation time length to be relatively long to make the velocity-detection sensitivity at each instance of sampling higher, allowing for the easy detection of the waveform, even though the waveform becomes slightly leveled in the time direction. Meanwhile, in the measuring phase for measuring a diagnostic index based on the detected waveform data, it is desirable to set this observation time length to be relatively short to increase the time resolution of the waveform. However, conventional ultrasonic diagnostic devices do not provide such a function for switching the observation time length. Therefore, in the present circumstances, the observation time length is set to be relatively short starting at the detecting phase, while the velocity-detection sensitivity is left to decrease in spite of the detection of waveforms, resulting in that much more time spent detecting the waveforms.